11. Efficient and final causes
1. The efficient cause
Things have been made by someone or something, i.e., things do not come out of the blue. For instance, a hybrid car is moved by petrol or diesel and electricity, and has been produced by someone: engineers and workers of a factory. This something or someone that produces things is the efficient cause.
The efficient cause converts into actual what was previously potential. It makes something to change from potentiality to actuality. For instance: the wood of a tree is potentially a table. Carpenter takes the wood and makes the table. Carpenter is the efficient cause. Another example: a watchmaker (efficient cause) can take the small wheels and pieces of a watch and after putting them in order, assemble it.